The Effect of Disturbance and Freshwater Availability on Lower Florida Keys’ Coastal Forest Dynamics

Authors

Danielle E. Ogurcak, Florida International UniversityFollow

Document Type

Dissertation

Degree

Doctor of Philosophy (PhD)

Major/Program

Geosciences

First Advisor's Name

Michael S. Ross

First Advisor's Committee Title

Committee chair

Second Advisor's Name

Joyce Maschinski

Second Advisor's Committee Title

Committee Member

Third Advisor's Name

René M. Price

Third Advisor's Committee Title

Committee Member

Fourth Advisor's Name

Leonel Sternberg

Fourth Advisor's Committee Title

Committee Member

Fifth Advisor's Name

Dean Whitman

Fifth Advisor's Committee Title

Committee Member

Sixth Advisor's Name

Keqi Zhang

Sixth Advisor's Committee Title

Committee Member

Keywords

Coastal Forests, Lower Florida Keys, Disturbance, Freshwater Lens, Sea Level Rise, Hurricane Storm Surge, Salinity, Precipitation, Remote Sensing, Stable Isotopes

Date of Defense

11-6-2015

Abstract

Coastal forest retreat in the Florida Keys during the 20^th century has been attributed to a combination of sea level rise and hurricane storm surge impacts, but the interactions between these two disturbances leading to forest decline are not well understood. The goal of my research was to assess their effects over a period spanning more than two decades, and to examine the relationships between these press and pulse disturbances and freshwater availability in pine rockland, hardwood hammock, and supratidal scrub communities. Impacts and recovery from two storm surges, Hurricanes Georges (1998) and Wilma (2005), were assessed with satellite-derived vegetation indices and multiple change detection techniques. Impacts were greater at lower elevations, and in hardwood hammock, spectral signatures indicative of plant stress and productivity returned to pre-disturbance levels within a few years. In pine rockland, impacts were predominately related to Hurricane Wilma, however, a similar return to pre-disturbance conditions was absent, suggesting that trajectories of disturbance recovery differed between the two communities. Long-term monitoring of forest composition, structure, and groundwater salinity showed that compositional shifts in the low shrub stratum were associated with salinization of the freshwater resource attributable to sea level rise. Throughout the course of twelve months of climate and groundwater monitoring (2011-2012), groundwater salinity generally decreased in response to large precipitation events. Modeling of geophysical data indicated that groundwater salinity was an important predictor of community type. Isotopic analysis of d¹⁸O in plant stem water and foliar d¹³C was used to determine temporal and spatial patterns in water use and plant stress in two community dominants, slash pine, Pinus elliottii var. densa, and buttonwood, Conocarpus erectus. Both species relied heavily on groundwater, and plant stress was related to increasing groundwater salinity. The results of this work suggest that the interaction of press and pulse disturbances drive changes in community composition by causing mortality of salt-sensitive species and altering the freshwater resource.

Identifier

FIDC000187

Recommended Citation

Ogurcak, Danielle E., "The Effect of Disturbance and Freshwater Availability on Lower Florida Keys’ Coastal Forest Dynamics" (2015). FIU Electronic Theses and Dissertations. 2288.
https://digitalcommons.fiu.edu/etd/2288